Best Auto Top Off System - Keeping Your Aquarium Stable (2020 Reviews 🏅)

October 20, 2019

Best Auto Top Off System - Keeping Your Aquarium Stable (2020 Reviews 🏅)

Aquarium automation is becoming more and more of a reality to the modern aquarist these days. One of the most common applications of tank automation are auto top of systems (AKA ATOs). These systems work to add freshwater to your aquarium as water evaporates. In saltwater tanks, they are extremely valuable in maintaining stable salinity levels as salinity can swing as water evaporates and does not get replaced. In freshwater tanks, this will keep your water level stable so your filtration can run optimally and so your tank doesn't completely dry out.

Replacing evaporated water can be a real pain, especially for those with larger aquariums. Auto top off systems make things easy for you to manage without carrying a bucket of water everyday. However, you have to be very diligent about the system you choose. Auto top off systems can be finicky and selecting one of poor quality ones can lead to a tank disaster and possibly an expensive home repair bill!

This is the reason for this post today. Auto top off systems are great tools for making your life easier, but not all auto top off systems are created equal. I've used or have experience with most of these top off systems I will go over today. Before we get started, let's talk about why a top off system is so great and what features you should be looking for.

Why Do You Need An Auto Top Off System? 

Anyone with a large amount of money invested in an complete aquarium system wants to protect their investment. An auto top off system is an automation tool that maintains stability in your aquarium. With saltwater aquariums it can not only be used keep your salinity levels stable, but also to add supplements to your reef tank via Kalkwasser. In freshwater systems, it will keep your levels stable for equipment to run correctly.

The main thing with an auto top off system is that you need a reservoir of water to pull from. You can use a sample 5 gallon bucket, brute trash can, or a glass/acrylic top of container designed for aquarium usage. The reservoir will usually last 5-7 days before needing to be filled up again saving you the time from having to fill up water manually. Auto top off systems are also very valuable if you are out of town or frequently away and can't regularly maintain the tank's water level.

Choosing An Auto Top Off System (What To Look For)

Auto top off systems are widely available in the hobby and there are several cheaper options like a DIY systems, however we have to outline the major critical features that are required in a quality system. Below are the main things we want when selecting a proper top off system for our aquariums:

Redundancy (Fail Safes)

This is the most important feature to look for. Auto top off failure is pretty common, especially with systems that use a manual float switch. If the switch fails, the top off system will fail to turn off, which causes too much water to be added. Ideally, we need dual sensors with our auto top off system. We also desire both a manual and digital sensor. 

Aquarium Float Switch

For a manual sensor we want a float switch (pictured above). The float switch has a switch that floats with the water level in your aquarium. As the water level rises the switch triggers and turns off the top off system. This the most common type of top off switch and something you may be familiar with if you have seen the float switches on your toilets. They are fairly reliable, but since it has moving parts they are prone to getting clogged with salt creep, getting jammed with critters like inverts, getting interrupted by waves, or breaking.

Auto Top Off System Digital Sensor

For a digital sensor (pictured above), we want an electronic eye sensor. This sensor monitors the water level in the aquarium and turns off the top off system electronically when the eye senses water above where it's set. It is reliable, but prone to getting clogged up by water impurities over time. Most top off manufactures like to market these sensors as "not having moving parts" knowing that manual switches can fail, but don't really like to mention the faults of a digital switch.

This is why we want to have a system with both manual and digital sensors. We can live with a dual manual or digital sensor, but the best of both worlds is a combo of digital and manual as both sensors can fail for different reasons.

Auto Shut Off Timers

Another critical feature we are going to want is a auto top off system with an auto shut off timer. In the event of a switch failing, an auto top off system with a shut off timer will shut off the pump before a major water disaster can occur. One of the biggest concerns with a DIY ATO solution is that there is no auto shut off timer. This means that water will continue to fill in your aquarium if your switches fail. This can be disastrous not only to your aquarium, but also to your home as well! You would have to add some type of auto shut off feature on a DIY system or consider an aquarium controller, both of which will add costs to the system.

The Best Auto Top Off Systems For Your Money

Now that we know what we are looking for. Let's look at the best auto top off systems available on the market. Just so you know, Aquarium Store Depot may collect a share of sales or other compensation from the links on this page (learn more).

In this list, we are looking for systems with all the desired features we mentioned above.

Picture Name Sensor Types Links
Hydor Auto Top Off System Hydor Smart Level Controller Digital (Dual)

Ice Cap ATO IceCap ATO  Digital (Dual)

JBJ Auto Top Off JBJ Auto Top Off Manual (Dual)
Tunze Osmolator Tunze Osmolator Digital and Manual

XP Aqua Duetto Auto Top Off System XP Aqua Duetto ATO Digital (Dual)


1) Hydor Smart Level Controller - Dual Sensor ATO For A Reasonable Price

Hydor Smart Level Controller Review


The Hydor Smart Level Controller is an ATO system that uses a dual sensor to manage your aquarium's water level. The sensors are included on a single plug making it easy to install. It is a sump based ATO systems, so I would not recommend it for using it in tank as the alarm level is set very high if used in an aquarium. It features a dual alarm system with both lights and sound. The sensors are not affected by waves in the tank.

What I don't like about this auto top off system is that it does not come with a pump. You have to purchase that separately so the price may not be as great as it seems if you pick up a more expensive pump. The switch holder is also a hybrid suction/magnet. I would prefer a true magnet mount.


  • Reasonable Price
  • Alarm
  • Dual Sensors


  • No Manual switch
  • Not a True Magnet switch holder
  • No Pump included!

2) IceCap ATO - Reliable Dual Sensor System

IceCap ATO Review

The IceCap ATO is a comprehensive top off system that includes dual digital sensors. These dual digital sensors read your water level and provide a min and max sensor. This provides a dual sensor back up for the auto top off unit. CoralVue advertises this unit as one without moving parts. It is a bit of marketing fluff to do this, but overall it is a competent unit for the price.

The pump that is included is of good quality and it is mounted with magnets, which I feel is a better and more secure mount than the Hydor system. The alarm has a nice feature that lets you when your reservoir is low, which helps when you don't look at the ATO container. CoralVue is a brand is also known for quality customer service so that's another thing that gives this system a leg up.

It has a decent price for what it offers. It lacks a manual switch and a shut off feature but overall it is a good package for the price.


  • Reasonable Price
  • Dual Sensors


  • No Manual switch

3) JBJ Auto Top Off - Budget Friendly ATO

JBJ ATO Review)

The JBJ Auto Top Off system is one of the main time tested entry level auto top off systems on the market. This system is different than the others before it on this list as it features two manual float switches that will trigger as your water level rises. There are no of digital sensors on this auto top of system. I actually don't mind the dual float sensors and with the two types of setups you can do with this ATO system, you can have a pretty full proof and redundant system. 

Another great feature is this system is easy to customize. You can modify the auto shut off timer by upping the time on the controller and tuning the shut off with a screw driver and you can also turn on an alarm when the ATO turns on. That's a really great feature for control and to prevent any flooding in the event the float switches fail.

The controller features an audible alarm if the max float switch triggers and both float switches are reversible if you need to do that. It really offers a lot for its price point.

The things I don't like with this system is you have to purchase a pump and the mount options aren't that great. There is a suction cup mount option, which I would not recommend, and the bracket mount options just don't look very pleasing to the eye and may mount weird if you have a rimless tank or sump. Not having a pump included usually brothers me with auto top off systems. I tend to lean on systems that comes with pumps as it takes out any guesswork I need to do.


  • Reasonable price
  • Easily modifiable and customized
  • Auto shut off feature


  • Suction cup mounts (Use brackets instead!)
  • No pump included

4) Tunze Osmolator 3155 - The Gold Standard of ATO Systems

Tunze Osmolator Reviews

The Tunze Osmolator is without a doubt the gold standard for auto top off systems in the industry. It has everything that I listed earlier that we are looking for in an ATO system. It has dual sensors - one float switch and one digital sensor that work together to manage your water level. It has an auto shut off feature so you won't have to worry about the pump running too long or your house flooding if the switches fail. It has an audible alarm if the water level gets too high and comes with a quality pump from Tunze.

The Tunze brand is well known for building lasting equipment and the reputation of this auto top off system is well known. They last for years and rarely fail with the pump usually failing first and being easy to replace. This is the ATO of choice for anyone building a quality display tank. You may have noticed there is a nano osmolator available from Tunze - but it's simply not the same as it only has one sensor and I only list dual sensor ATOs for a reason on this post.

It comes with a high price though. It's the most expensive auto top off system for a reason. You get what you pay for with this system.


  • Manual and digital sensors
  • Proven reputation and name brand in Tunze
  • Quality pump included
  • Auto shut off feature


  • Expensive
  • Pump can be a little loud

5) XP Aqua Dueletto ATO - Build for All In One Systems

XP Aqua Dueletto ATO Review

The XP Aqua Duetto ATO system is an ATO that has been designed with all-in-on aquariums in mind. It is designed for this purpose so well that Waterbox Aquariums often sells this ATO as an add on to their reef ready system. It is marketed as the "world's smallest dual-sensor aquarium top-off system" and you can see by the sensors and pump how small it really is. It can achieve this small footprint by not using moving parts, opting for a digital sensor setup.

The pump is a DC pump, which draws less power and allows it to be smaller in size. So small that it can easily fit in all-in-one chambers and operate effectively. It uses dual digital sensors that will work in complete darkness. Because the sensors mount magnetically without a sensor mount, they can be placed just about anywhere in the aquarium or sump chamber and can be hidden easily.

For those aquarists who want a compact version of an osmolator, XP offers an ultimate version with 4 sensors that competes with the Osmolator 3155


  • Small enough for all-in-one tanks
  • Good purchase considering pump is included


  • Only uses a digital sensor
  • No auto shut off feature

What is the Best Auto Top Off System (Our Recommendation)?

If you want the best quality and most reliable auto top off system, my recommendation is very simple. It would be the Tunze Osmolator 3155. It's ironclad reliable, will service your tank for years, and is built very well. If that is not in your budget, I would recommend the XP Aqua Duetto Auto or JBJ Auto Top Off depending on if you have a pump available or not. The XP Aqua offers a good price and includes the pump and is reliable. The JBJ is cheap if you have a pump and has adjustable features when you access the inside of the controller. 

How to Setup An Auto Top Off System

ATOs are actually really easy to install. They are probably one of the easiest tank automation tools to maintain and install on an aquarium. This video below shows how to install an XP Aqua Ultimate on a sump system. The install would be very similar installing an ATO in the display tank or all in one aquarium. 

For the reservoir you will want to use a food grade bucket or trash can or an acrylic or glass ATO container. If you are running a saltwater tank, you will want to use RODI water from an RODI System. Make sure to fill up the reservoir and put the pump in the container before you turn on the system so the pump does not run dry.

Conclusion On Best Auto Top Off Systems

Auto top off systems can be great great automation tools are are really a requirement if you want to keep an aquarium system that is demanding like a reef tank. Careful research and consideration is needing when selecting the right unit for you and I hope I made your buying decision easier with the overview of the systems and recommendations. If you have any questions, please leave a comment below. Thanks for reading.

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